1. Field of the Invention
The present invention is generally related to a shift mechanism for a marine propulsion system and, more particularly, to a cam and cam follower arrangement which improves the efficiency of the shift mechanism and allows the arrangement of components to be reversed in order to accommodate a shift control mechanism on either the port or starboard side of the marine propulsion system.
2. Description of the Prior Art
Many different types of shift mechanisms are known to those skilled in the art for use in conjunction with marine propulsion systems, such as outboard motors or sterndrive systems.
U.S. Pat. No. 4,223,773, which issued to Croisant et al on Sep. 23, 1980, discloses a drive engaging apparatus. A clutch apparatus for a marine drive lower gear case includes a propeller shaft rotatably mounted in a gear case housing. A drive gear for both forward and reverse is positioned in the housing coaxial with the propeller shaft and a clutch member is rotatably fixed on the propeller shaft and moveable axially into drive engagement with the drive gear. Clutch engaging elements are provided on opposed portions of the drive gears and the clutch member. Shift means utilizing a positive acting cam means positively move the clutch member into and out of engagement from the drive gears. The shift means also include a releasable latch means to positively maintain the shift means in the engaged position and a preloading means between the shift means and the clutch member to snap the clutch member into engagement.
U.S. Pat. No. 6,062,360, which issued to Shields on May 16, 2000, discloses a synchronizer for a gear shift mechanism for a marine propulsion system. A synchronized gear shift mechanism is provided for a marine propulsion system. Using a hub and a sleeve that are axially moveable relative to an output shaft but rotationally fixed to the shaft and to each other, the gear shift mechanism uses associated friction surfaces to bring the output shaft up to a speed that is in synchronism with the selected forward or reverse gear prior to mating associated gear tooth surfaces together to transmit torque from an input shaft to an output shaft. The friction surfaces on the forward and reverse gears can be replaceable to facilitate repair after the friction surfaces experience wear.
U.S. Pat. No. 4,986,774, which issued to Wantz on Jan. 22, 1991, discloses a desmodromic shift adaptor for a counter-rotating propeller shaft assembly. An adaptor member is described for accommodating the use of a desmodromic cam-actuated shifting mechanism into a conventional propeller shaft cavity formed in the lower end of the gearcase of a marine propulsion system, wherein forward thrust on the propeller shaft is transferred to the gearcase at a point aft of the forward and reverse gears mounted about the propeller shaft. The adaptor member includes a cup, which is adapted to mount the fore one of the forward and reverse gears through a bearing member. The adaptor member further includes an internal passage within which is disposed the movable cam of the shifting mechanism, and an opening is in communication with the passage for allowing connection of the shift shaft to the shifting cam after assembly of the adaptor member into the gearcase cavity.
U.S. Pat. No. 5,788,546, which issued to Ogino on Aug. 4, 1998, describes a shift assistor for a marine transmission. A transmission for a dual, counter-rotational propeller system incorporates a shift assistor to yieldably cushion transmission engagement. The shift assistor desirably operates between one clutch of a dual clutch assembly and a clutch actuator. The shift assistor specifically yieldably couples the clutch to the actuator. The yieldably coupling permits relative movement between the shift assistor and the clutch during the shifting operation in order to allow the clutches to engage the corresponding gears separately. The shift assistor thus reduces coupling shock when shifting the transmission either into a forward or a reverse drive condition.
U.S. Pat. No. 5,910,191, which issued to Okamoto on Jun. 8, 1999, describes a shifting mechanism for an outboard motor. An engine of an outboard motor includes an improved engine component layout to minimize the size of the engine and to generally isolate a shift position mechanism from an intake air flow into the engine. The outboard motor includes a shifting mechanism that shifts a transmission between three operational states: forward, neutral, and reverse. The shifting position mechanism is principally positioned directly beneath a flywheel of the engine. The position simplifies the design of the shifting mechanism and reduces the girth of the engine and associated components within the cowling.
U.S. Pat. No. 5,059,144, which issued to Onoue on Oct. 22, 1991, describes an ahead/astern shifting device for a marine propulsion unit. A shift arrangement for a marine outboard drive that permits a forward positioning of the drive shaft without interfering with the operation of the shifting mechanism is disclosed.
U.S. Pat. No. 4,412,826, which issued to Jones et al on Nov. 1, 1983, describes a safety shift device for an outboard motor. A device is disclosed for attachment to the gear shift lever of an outboard motor to enable shifting the gears from neutral to forward and/or reverse at a safe distance inboard of the motor.
U.S. Pat. No. 5,310,370, which issued to Onoue on May 10, 1994, describes a thrust supporting structure for a marine propulsion unit. A thrust taking arrangement for a marine propulsion unit that employs a propeller shaft and a thrust transfer member that is affixed against an abutment on the propeller shaft and which transfers thrust to a lower unit housing through forward and reverse thrust bearings. In one embodiment, the thrust transfer member is permanently affixed to the propeller shaft and in the other embodiments, it is detachably connected by threaded connections.
U.S. Pat. No. 5,839,928, which issued to Nakayasu et al on Nov. 24, 1998, describes a shifting mechanism for an outboard drive. A shifting mechanism for an outboard drive of a watercraft provides reduced coupling shock when the forward gears are engaged by a dual clutch assembly, as well as provides for consistent and quick engagement of the clutch assembly with the gear. The shifting mechanism involves a first gear and a corresponding first clutch, and a second gear and a corresponding second clutch. A plunger carries the first and second clutches which are arranged on the plunger at unequal distances from their respective gears. This nonuniform spatial relationship between the clutches and gears causes one clutch to engage its corresponding gear before the other clutch engages its corresponding gear. The staggered engagement decreases shock on the transmission and permits quicker engagement between the clutches and gears.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The patents described above illustrate many different versions of gear shift mechanisms and apparatus for use in a marine propulsion system. For example, U.S. Pat. No. 4,223,773 discloses a desmodromic actuator mechanism to move a clutch member axially in a direction parallel to a propeller shaft axis and into and out of engagement with forward and reverse gears. U.S. Pat. No. 5,910,191 shows the general arrangement of the shift mechanism in relation to other structures in the outboard motor. U.S. Pat. No. 5,059,144 shows one possible configuration of a cam and cam follower arrangement for a shift mechanism of an outboard motor. U.S. Pat. No. 4,412,826 shows the general configuration of a shift lever on the starboard side of an outboard motor cowl.
A shift mechanism for a marine propulsion system, made in accordance with the preferred embodiment of the present invention, comprises an output shaft which is rotatable about a first axis and a first drive gear which is rotatable about the first axis and also rotatable relative to the output shaft. A clutch member is rotatable with the output shaft about the first axis and is movable relative to the output shaft in a direction parallel to the first axis. An actuator is attached to the clutch member for axial and rotational movement in synchrony with the clutch member. A cam, which is rotatable about a second axis, is shaped to have a protrusion extending in a direction away from the second axis. The cam has a cam surface proximate a distal end of the protrusion. A cam follower is attached to the actuator. A first channel is formed in the cam follower and is generally perpendicular to the first axis. The channel extends between a first pair of cam follower surfaces in a first direction away from the first axis. The protrusion extends into the first channel and between the first pair of cam follower surfaces. The actuator is movable in an axial direction in response to rotation of the cam about the second axis.
In a preferred embodiment of the present invention, a second channel is formed in the cam follower and is generally perpendicular to the first axis. It extends between a second pair of cam follower surfaces in a second direction away from the second axis. The second direction is generally opposite and parallel to the first direction. The protrusion is alternatively disposable into the first and second channels and between the first and second pairs of cam follower surfaces.
The actuator and the cam follower are rotatable relative to each other and movable in synchrony with each other in a direction parallel to the first axis in a preferred embodiment of the present invention. The first drive gear can be a forward gear or a reverse gear. A second drive gear, which is rotatable about the first axis and rotatable relative to the output shaft, can also be provided in which the clutch member is alternately movable relative to the output shaft in a direction parallel to the first axis and into driving relation with the first or second drive gears.
The output shaft can be a propeller shaft and the marine propulsion system can be an outboard motor. The protrusion of the cam can comprise a generally spherical cam surface or, alternatively, the cam surface can be shaped to conform to an involute surface. Other shapes of the cam surface are also compatible with the concepts of the present invention.